Human monocytes have been removed from the peripheral blood of normal volunteers and cancer patients for study in a wide range of immunologic assay systems. The technique of countercurrent centrifugal elutriation has been applied to these cells to generate as many as 10 to the 9th power 95% pure cells. In addition, lymphocytes that are completely monocyte-depleted can be obtained by the same technology. Elutriation generates cells that are in suspension; we have developed techniques to maintain these cells in suspension culture using serum-free media and specially developed Teflon labware. Thus, these cells are thought to be most representative of the native state of monocytes in the bloodstream. These cells have been studied with regard to their accessory cell functions for human lymphocytes, their MIF activity and chemotactin activity, their ability to release biological response modifiers (including colony stimulating factor, interferon, fibroblast growth factor, prostaglandins and soluble cytotoxic factors); in addition, the tumoricidal activity of these cells in antibody-dependent cellular cytotoxicity and spontaneous cytotoxicity assay systems has been measured. Having documented the tumoricidal activity of elutriator-purified monocytes, we have initiated attempts to utilize large numbers of these cells in an adoptive transfer setting in patients with peritoneal carcinomatosis; these patients received weekly administration of their own elutriator-purified monocytes (activated with Gamma-interferon) into their peritoneal cavity via an indwelling Tenckhoff catheter.